Two-stage hydraulic amplifier



Jan. 8, 1952 E. R.- WALTHERS 2,582,088

TWO-STAGE HYDRAULIC AMPLIFIER Filed Nov. 1, 1947 37 38 Fig 7 a9 40 8 43 ze 2 r3 I i "1 I J 1 l I I I x. l

,'-Full Pressure ,"Pf G) 32- g; Inventor:

Earle n. Walthers, D Pr- W I left neutral right ram assure IU gu W His Attorne s.

Patented Jan. 8, 1952 TWO-STAGE HYDRAULIC ALIPLIFIER Earle R. Walther-s, Schenectady, N. Y., assignor to General Electric Company, a corporation of New Iork Application November 1, 1947, Serial No. 783,516

9 Claims. 1

The present invention relates to hydraulic control apparatus and more particularly to apparatus for selectively controlling the rate of fluid flow from a source of fluid pressure to either of a pair of conduits, such. as the fluid connections to a servomotor.

Heretofore, it has been customary to provide hydraulic control apparatus having amplifying means to move a main control valve by. the operation of a pilot or auxiliary valve. Generally the amplifying means takes the form of a pair of cylinders and pistons which are arranged to move the main valve and are connected by fluid conduits to the auxiliary or pilot valve which selectively connects the conduits to either the fluid pressure source or drain. In this way, the main valve is operated by the fluid pressure which in turn is controlled by the auxiliary valve so that the force required to operate the auxiliary valve is only a fraction of that required to move the main valve, and only a small controlling force is therefore required to obtain movement of the main valve. However, these arrangements have the disadvantage in that when the auxiliary valve is opened a small amount, the main valve is moved to either a completely on or a completely ofi position so that there is no proportional movement of the main valve with respect to the movement of the auxiliary valve. With the arrangement of an auxiliary valve to move the main valve control member it is difllcult to obtain any movement of the main valve except the above-referred to on"off movement unless the pressure of the operating fluid is carefully controlled and proportioned to a centering force on the main valve control member such as the force available from centering springs.

Heretofore, it has also been the practice to use a mechanical linkage between the auxiliary valve and the main valve when it was desirable to obtain a proportional movement of the main valve with respect to the auxiliary valve. However, these mechanical linkages permit undesirable leakage and further complicate operation of the apparatus.

It is therefore an object of my invention to provide an improved hydraulic control apparatus in which the movement of a main valve is proportional to the direction and magnitude of the displacement of an auxiliary valve.

A further object of my invention is to provide control apparatus in which the displacing force on the main valve is proportional in direction and magnitude to the displacing force on the auxiliary valve.

Fig. 1 is a. cross sectional view of hydraulic control valve apparatus embodying my invention with the output conduits connected to a hydraulic servomotor.

Fig. 2 is a graph of the operating pressures in the pressure sensing lines 3| and 32 when the auxiliary valve is moved from center or neutral position.

Referring now to Fig. 1, there is shown 9. casing I having a fluid pressure supply line 2, a pair of output conduits 3 and 4 and four fluid drain connections 5, 6, l and 8. To supply fluid under pressure to both a main valve and an auxiliary valve, the fluid conduit 2 is connected to passage 9 which in turn communicates with a distribution chamber l0 surrounding the center land of the auxiliary valve. From chamber Ill fluid under pressure is admitted through passage H to chamber l2 surrounding the center land of the main valve. A pair of through bores l3 and M respectively intersecting the chambers l0 and I2 are provided for the three-land control members l5 and I 8 respectively reciprocable in bores I3 and M. The fluid drain conduits 5 and 6 are respectively connected to passages I! and I 8 which in turn communicate with bore l4 and are normally adapted to be covered by the outer lands of control member l6 of the main valve. In order that control member It may selectively connect output conduits 3 and 4 to either fluid pressure supply chamber l2 or to drain passages H or to, a pair of passages l9 and 2B are connected between the output conduits 3 and 4 and the recessed portions of the control member l6. For the purpose of centering the main valve control member it in a neutral position, I have provided spider springs 2! and 22 and threaded stub shafts 23 and 24 which are held by the springs and are adapted to engage the ends of control member l6. Adjusting nuts 25 and 2B are provided on the stub shafts for adjusting the position of control member l6 and the centering force on the control member. In order to move the main valve control member from the neutral, or center, position, piston means have been provided such as pistons 21 and 23 respectively reciprocable in cylinder means 29 and 30. A pair of pressure sensing lines 3| and 32 for supplying fluid under pressure to cylinder means 29 and 30 respectively are connected between the cylinders and the bore l3 opposite the recessed sections of auxiliary control member |5.

Heretofore, it has been customary to displace the main valve control member IE from its centered or neutral position by selectively connecting either line 3| to the fluid pressure source and line 32 to drain, or reversing these connections to operate pistons 21 and 28. However, as mentioned before, these connections will provide only a completely on or of! positioning of control member l6 unless the pressure of the motive fluid is carefully proportioned to the tension on centering springs 2| and 22. To overcome this on-oil." movement of member l6 and to make the movement proportional to the magnitude of the movementof auxiliary control member |5. I have provided pressure controlling means adapted to apply pressure to lines 3| and 32 proportional in direction and amount to the movement of member l from its centered or neutral position. This pressure controlling means is provided by a pair of bypass conduits 33 and 34 connected between bore l3 and drain passages 35 and 35. Passages 35 and 36 in turn communicate with the drain connections I and 8 and also with the respective ends of bore |3. The end lands of control member l5 are normally positioned to cut off direct communication between bore I3 and passages 35 and 36. However, it will be noted that the center land of the control member I5 is underlapped so that fluid under pressure in chamber In is permitted to enter here |3 around the under cut portions of control member 15 on either side of the center land. This fluid under pressure in chamber I3 passes to the drain passages 35 and 36 through bypass lines 33 and 34. Adjustable needle valves, such as members 31 and 38, are fixedly mounted in lines 33 and 34 respectively to reduce fluid pressure to the lines 3| and 32, by allowing a restricted flow of fluid through an orifice to the passages 35 and 35. Nuts 39 and 40 are provided on needle valves 3! and 38 to lock the valves in place.

In order to center control member I5 and displace it in either direction from the center or neutral position, I have provided an electrically operated solenoid member 4| having a core 42 provided with a threaded shaft extending through both ends of the core 42. The core is adapted to be centered with respect to the coil 43 and with respect to the control member l5 of the auxiliary valve by spider springs 44, 45 and stub shaft 46, which bears against the opposite end of control member |5. Spider spring 41 positions stub shaft 46 to assist the centering action of control member l5 and solenoid core 42. Adjusting nuts 48, 48 and 50 are provided at each of the spider springs to regulate the spring force for centering control member 15 and solenoid core 42.

This control apparatus may be used in socalled fail safe applications in which it would be desirable to shut off the function under control in case of failure of electrical power to the solenoid 43. To provide for such a contingency, either the main valve |6 or the auxiliary valve 4 I5 may be adjusted to be ofi center when no power is supplied to the solenoid 43 by means of the adjusting nuts 24 and 25 and 48 and 49 respectively.

Due to the leakage of fluid under pressure between pistons 21 and 28 and their respective cylinders 29 and 38, a passage 5| has been provided to equalize the pressures between chambers 52 and 53, which are adjacent the ends of the main valve control member. Passage 5| is provided to prevent possible false operation of the control member in the event that the pressure in one of the chambers 52 or 53 exceeds that in the opposed chamber. A similar passage 54 is provided for a like purpose between chambers 55 and 56 at the ends of the auxiliary valve control member 5.

In Fig. 2 I have shown a graphical representation of the proportional characteristic produced in lines 3| and 32 by plotting the movement of auxiliary valve control member i5 versus the pressures in lines 3| and 32. As shown, pressures Pi and P2 representing the pressures in lines 3| and 32, respectively, are equal when control member H3 is in the neutral or centered position. However, when member is is displaced to the left from the position shown in Fig. 1, pressure P1 decreases while pressure P2 increases a corresponding amount thereby producing a diiferential pressure between the lines 3| and 32'which is proportional to the amount of displacement of member |5. With control member |5 displaced to the right a difierential pressure in the opposite direction or sense is developed between the lines 3| and 32. This differential pressure is likewise proportional to the amount of displacement of the control member.

If there were no resisting force to the pressure difl'eerntial between Pi and P2, the valve |6 would be moved to the limit of its travel accordin to the direction of the pressure diflerential. The spider springs 2| and 22 provide the biasing force necessary to resist this pressure differential in order to maintainthe movement of the valve l6 proportional to that of the auxiliary valve |5. Adjustment of the spider springs is made to coordinate maximum opening of the valve |6- with maximum travel of the valve |5.

The auxiliary valve l5 shown in Fig. l of the drawing, has an underlapped center land and exhaust lands that have no lap. With the auxiliary valve I5 in the neutral position, the pressures P1 and P2 are equal at the higher value as shown in full in Fig. 2, since there are orifices at each end of the center land through which fluid can pass into the conduit l3. The dotted lines of Fig. 2 represent the comparative pressures in the sensing lines 3| and 32 when the center land has substantially no underlap and are designated Pi, and P2. For this condition Pi and P2 are equal at the center position of the valve but the orifices around the ends of the center land are smaller than they are in underlapped construction.

If the center land were overlapped, the point of equal pressure would be still lower on the line representing the neutral valve position since the leakage to the conduit |3 would be still less.

Operation of my control apparatus is as follows; With the auxiliary control member |5 in a centered or neutral position, fluid under pressure entering through conduit 2 flows to chamber ill and then throu h the passages 33 and 34 into drain passages 35 and 36 respectively at the same aoeaoes rate .of flow. Due to the flow through passages 33 and 34 fluid pressures will be established in pressure sensing lines 3| and 32 dependent upon the rate of flow through passages 33 and 34. With control member l5 in the centered or neutral position, it will be understood that the pressures in the passages 3| and 32 will be equal and with these equal pressures applied to pistons 21 and 28 respectively the control member l6 of the main valve will be held in its centered position so that there is no fluid flow to output conduits 3 and 4. However, with an electric signal applied to coil 43 of solenoid 4| as by increasing the cur rent supplied to the coil, core 42 is moved to the left as viewed in Fig. 1, thereby moving control member l5 likewise to the left. In this way the fluid pressure in chamber Ill is more readily admitted to passage 34 and simultaneously the flow to passage 33 is reduced so that a higher pressure is developed in line 32 than that produced in line 3|. Accordingly, the control member I6 is moved to the lei t thereby connecting passage 20 and output conduit 4 to the fluid pressure supply chamber I2 while at the same time opening output conduit 3 to drain line 5 through the bore 14.

The control member 16 of the main valve may be made to operate in the reverse direction thereby reversing the connections to output conduits 3 and 4 by decreasing the current supplied to coil 43 and thereby moving control member ii of the auxiliary valve to the right and increasing the rate of flow through passage 33 and, at the same time, reducing the flow through passage 34. Due to the fact that pressure sensing lines 3| and 32 are not directly connected either to the fluid pressure supply line or the drain lines a proportional movement of the main valve control member 16 is. obtained rather than" an on-ofi action, which would be produced by directly connecting the pressure sensing lines with the supply force pressure or to drain. However, since lines 3! and 32 are adapted to sense the pressure in lines 33 and 34 a proportional control of the main valve is obtained relative to the direction and magnitude of the displacement of the auxiliary control member l5. In this way the rate of fluid flow to output conduits 3 and 4 may be closely regulated and such rates of flow made proportional to the electrical signal applied to the control solenoid.

It will be understood by those skilled in the art I that this ability to control the rate of fluid flow to output conduits 3 and 4 in proportion to the signal applied to an electrical control solenoid is particularly useful in controlling the movement of a servomotor since the speed of the movable member of the servomotor is dependent upon the rate of flow of the motive fluid.

It will also be understood that various modifications may be made in the construction of the control apparatus such as using the ends of the control member It as the operating pistons for the main valve. While separate drain lines 5, 6, l and 8 have been shown in the preferred embodiment for the sake of clarity, it will be apparent that these linesmay be interconnected within the body of the valve and a single drain .connection provided to casing I.

While I have illustrated and described a particular embodiment of my invention, modifications thereof will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not to be limited to the particular arrangement disclosed, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Hydraulic control apparatus comprising a source of fluid pressure, a pair or fluid conduits, a pilot valve member connected between said conduits and said source for simultaneously varying the rate of flow of fluid from said source to each of said conduits, said pilot valve member including a center land for varying aninlet opening and two end lands for varying two discharge openings, the end land variable discharge openings being normally closed when said pilot valve member is in a central position, a flow restricting means fixedly mounted in each of said conduits, a main valve member for selectively connecting either of a pair of output conduits to said source, pressure responsive means for operating said main valve and a pair of pressure sensing lines between said pressure responsive means and the upstream side of the flow-restricting means in said fluid conduits whereby said main valve member may be moved in response to variations in flow in said fluid conduits.

2. Hydraulic control apparatus for selectively connecting either of a pair of fluid output conduits to a source of fluid pressure, said apparatus comprising a main valve between said output conduits and said source of fluid pressure adapted to be selectively operated by a pair of pressure responsive devices in accordance with the difference in pressure in a pair of pressure sensing lines wherein the pressures are varied in sense and magnitude by an auxiliary valve, said auxiliary valve being connected between said source of fluid pressure and a pair of fluid by-pass conduits to simultaneously change the rates of fluid flow through said fluid by-pass conduits, a flow restricting means mounted in each of said bypass conduits, the size of the passage through said restricting means being independent of the position of said auxiliary valve, said pair of pressure sensing lines being connected to said fluid by-pass conduits on the upstream side of said restricting devices whereby said differences in pressure are developed by said simultaneous changes in flow rate through said fluid by-pass conduits.

3. Hydraulic control apparatus comprising a main valve having a control member movable to connect either of two output conduits to a source of fluid pressure, means for biasing said control member to a predetermined initial position, a pair of pressure responsive devices connected to said control member for displacement thereof from said predetermined initial position, said pressure responsive devices being connected in opposed relation so as to move said control member in accordance with the sense and magnitude of the difference of two pressures applied re spectively thereto, an auxiliary valve connected to said source of fluid pressure, a pair of fluid by-pass conduits connected to said auxiliary valve each having flow restricting means positioned therein in displaced relationship to said auxiliary valve, an auxiliary valve control member movable to simultaneously and gradually vary in opposite directions the rates of flow through said fluid conduits and a pair of pressure sensing lines for separately subjecting said pressure responsive devices to the pressures in said fluid conduit on the upstream side of said flow restricting devices therein whereby said main valve control member is proportionally positioned in accordance with the displacement of said auxiliary valve control member from a balanced flow position.

4. Hydraulic control apparatus comprising a pair of fluid conduits connected to a fluid pressure source and having flow restricting means positioned in each of said conduits, pressure sensing lines connected to said conduits on the upstream side of said flow restricting means, an auxiliary valve having a control member connected between said conduits and said source in a position displaced from said flow restricting means for progressively varying the proportion 'of fluid flow from said fluid source to said respective fluid conduits whereby the pressure in said sensing lines may be varied in sense and magnitude in accordance with the displacement of said control member from a balanced flow position, a main valve adapted to selectively connect either of two output conduits to said fluid pressure source, biasing means for maintaining said valve in a predetermined initial P sition and a pair of pressure responsive devices connected to said pressure sensing lines and adapted to move said valve in accordance with the direction and amount of pressure difierence between said sensing lines whereby said main valve may be displaced from said predetermined position in proportion to the displacement of said 'auxiliary valve control member.

5. Hydraulic control apparatus comprising a main valve having a movable control member for connecting either 'of two output conduits to a source of fluid pressure, spring members for biasing said control member to a predetermined initial position, a pair of fluid conduits connected to said source of fluid pressure, each of said fluid conduits havin orifice means therein, an auxiliary valve including a control member connected between said conduits and said source in a position displaced from said orifice means for simultaneously and gradually varying in opposite directions the rates of flow through said fluid conduits, a control device for displacing said auxiliary valve control member in either direction from a balanced flow position, a pair of pressure sensing lines connected to said fluid conduits on the upstream side of said orifice means, cylinder means adjacent said main valve and connected to said sensing lines and pistons reciprocable in said cylinder means for moving said main valve from said predetermined position in accordance with the sense and magnitude of the difference in pressures in said sensing lines whereby said main valve control member may be displaced from said predetermined position in proportion to the direction and amplitudeof the displacement of said auxiliary valve from said balanced flow position by said control device.

6. Hydraulic control apparatus for selectively controlling the fluid flow from a source of fluid pressure to a pair of output conduits, said apparatus comprising a pair of fluid conduits connected to said source of fluid pressure, each of said conduits having flow restricting means therein, an auxiliary valve having a control member connected between said conduits and said source in a position displaced from said flow restricting means for simultaneously and progressively varying in opposite directions the rate of flow through said fluid conduits whereby movement of said control member from a balanced flow position produces an increase in pressure in one of said fluid conduits and a corresponding de-' crease in pressure in the other of said fluid conduits dependent upon the direction of said movement, spring members for biasin said valve to a predetermined initial position, solenoid means for displacing said valve in either direction from said initial position, a main valve for selectively connecting either of said output conduits to said source of fluid pressure, spring members for biasing said main valve to a predetermined initial position, a pair of cylinders in opposed relation having pistons reciprocable therein adapted to move said main valve in either direction from said predetermined position and a pair of pres sure sensing lines connecting said cylinders to said fluid conduits between said auxiliary valve and said flow restricting means whereby said main valve may be gradually moved in accordance with the sense and magnitude of the difference in pressure between said fluid conduits.

7. Hydraulic control apparatus comprisin a pair of fluid conduits connected to a fluid pressure source and having flow restricting means fixedly mounted in each of said conduits, pressure sensing lines connected to said conduits on the upstream side of said flow restricting means, an auxiliary valve having a control member connected between said conduits and said source in a position displaced from said flow restricting means for progressively varying the proportion of fluid flow from said fluid source to said respective fluid conduits whereby the pressure in said sensing lines may be varied in accordance with the displacement of said control member from a balanced flow position, a main valve having a control member for selectively connecting either of two output conduits to said fluid pressure source, means for biasing said main valve control member to a predetermined initial position and a pair of pressure responsive devices connected to said pressure sensin lines for moving said main valve control member in a direction corresponding to the sense of the pressure unbalance between said pressure sensing lines and in an amount proportional to the difference in pressures in said pressure sensing lines whereby said main valve control member may be con trollably positioned in accordance with the displacement of said auxiliary valve control member from said balanced flow position.

8. A two-stage hydraulic servo apparatus for controlling a hydraulic pressure fluid utilization device comprising a main servo valve for directly regulating the flow of hydraulic pressure fluid to the pressure fluid utilization device, piston means for positioning said main servo valve in accordance with a difference in two control pressures applied to said piston means, an auxiliary hydraulic servo valve for regulatin the pressures applied to said piston means including a center valve land for controlling the entrance of hydraulic pressure fluid into said auxiliary valve, end lands for controlling drain line connection openings at the respective ends of said auxiliary valve, pressure sensing conduits connected from said auxiliary valve at points between said center land and each of said end lands to said piston means, bypass conduits each having an adjustable restricted flow area connected from said auxiliary valve bore at positions between said center land and said end lands to drain line openings whereby the fluid pressure on each side of said auxiliary valve and the connected piston is dependent upon the flow of hydraulic pressure fluid into that side, a restricted pressure relievin outward flow being provided by said bypass pas sages.

9. A two-stage hydraulic servo valve apparatus for controlling the position or speed of a hydraulic pressure fluid utilization device comprising a. main servo valve having two outlet conduits for conveying hydraulic pressure fluid to the pressure fluid utilization device, said main servo valve being connected to a source of pressure fluid whereby movement of said valve in either direction from an initial central position connects said source of pressure fluid to one of said outlet conduits, a pair of opposed hydraulic pressure fluid actuatable pistons for positioning said main servo valve, the position of said main servo valve being determined in accordance with the difference in pressures applied to said pistons, an auxiliary hydraulic servo valve for regulating the pressures applied to said pistons including a central connection to said source of hydraulic pressure fluid, a center valve land for controlling the entrance of hydraulic pressure fluid from said source into said auxiliary valve, end lands for controlling discharge openings at the respective ends of said auxiliary valve, pressure sensing conduits connected from said auxiliary valve at points between said center land and each of said 10 end lands to said pistons, bypass conduits each having an adjustable restricted flow area connected from said auxiliary valve bore immediately adjacent each side of said center land to drain line openings whereby the fluid pressure on each side of said auxiliary valve and the connected piston is dependent upon the flow of hydraulic pressure fluid into that side, a restricted pressure relieving outward flow being provided by said bypass passages.

EARLE R. WALTHERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 901,613 Herrgott Oct. 20, 1908 1,897,386 Ferris Feb. 14, 1933 FOREIGN PATENTS Number Country Date 47,236 France Nov. 25, 1936 525,878 Germany June 9, 1931 

